JP2000077733A - Laminated piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability of a laminated piezoelectric element extending over a long period even under a high temperature, by a method wherein piezoelectric materials having a piezoelectricity and internal electrodes having a conductivity are alternately laminated to form integrally the piezoelectric materials, and the internal electrodes and stress relaxation layers are respectively formed on the vertical side surfaces of the laminated material in the lamination direction. SOLUTION: Piezoelectric materials 1 having a piezoelectricity and internal electrodes 2 having a conductivity are alternately laminated to form integrally the materials 1, the external electrodes 2 is connected to and the eternal electrodes 2 every other layer, and lead wires 4 are respectively connected with these electrodes 3. Moreover, stress relaxation layers 5, which are provided mixedly an inorganic porous material containing an silicon oxide as its main component with a conductive material containing conductive grains, such as silver grains palladium grains, are respectively formed between the materials 1 and the electrodes 3, between the electrodes 2 and the electrodes 3 and between insulating layers 8 formed on the electrodes 2 and the electrodes 3. As a result, even in the case where a laminated piezoelectric element is used extending over a long period under a high voltage, the reliability of the piezoelectric element can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laminated piezoelectric element used as an actuator or a sensor.

[0002]

2. Description of the Related Art As a structure of a piezoelectric element capable of mutually converting electrical energy and mechanical energy, a laminated piezoelectric element in which piezoelectric materials and internal electrodes are alternately laminated has been reported.

As an example, JP-A-6-232466 reports that a conductive portion containing glass frit is formed between an internal electrode and an external electrode.

[0004]

The multilayer piezoelectric element described in JP-A-6-232466 has a multilayer structure in which the amount of glass frit of a conductive portion formed between an internal electrode and an external electrode is gradually changed. Thereby, the two are suitably joined, but when used for a long time at high temperature, the multilayer is homogenized to become a single layer, and it is easier to break as compared to when used near room temperature. There is a problem.

An object of the present invention is to provide a piezoelectric element having high reliability even at high temperatures.

[0006]

A first aspect of the present invention for achieving the above object is as follows.
The feature of the present invention is that a stress relaxation layer is formed on a side surface perpendicular to the laminating direction in a laminated piezoelectric element in which piezoelectric materials having piezoelectricity and internal electrodes having conductivity are alternately laminated and integrated.

A second feature of achieving the above object is that a laminated piezoelectric element in which piezoelectric materials having piezoelectricity and internal electrodes having conductivity are alternately laminated and integrated is formed on a side surface perpendicular to the laminating direction. The stress relaxation layer has a structure in which an inorganic porous material and a conductive substance are mixed.

A third feature of achieving the above object is that a laminated piezoelectric element in which piezoelectric materials having piezoelectricity and internal electrodes having conductivity are alternately laminated and integrated is formed on a side surface perpendicular to the laminating direction. The thickness of the stress relaxation layer is smaller than 100 μm.

A fourth feature of achieving the above object is that a laminated piezoelectric element in which piezoelectric materials having piezoelectricity and internal electrodes having conductivity are alternately laminated and integrated is formed on a side surface perpendicular to the laminating direction. In other words, the conductive material constituting the stress relaxation layer contains conductive particles.

A fifth feature of achieving the above object is that a laminated piezoelectric element in which piezoelectric materials having piezoelectricity and conductive internal electrodes are alternately laminated and integrated is formed on a side surface perpendicular to the laminating direction. The particle size of the conductive particles contained in the conductive material constituting the stress relaxation layer is smaller than 5 μm.

According to a sixth aspect of the present invention, there is provided a fuel supply device for an engine using the laminated piezoelectric element according to the first to fifth aspects.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic sectional view showing the structure of a laminated piezoelectric element according to an embodiment of the present invention. In the laminated piezoelectric element of the present embodiment, the piezoelectric material 1 having piezoelectricity and the external electrode 3
Between the conductive internal electrode 2 and the external electrode 3,
The stress relaxation layer 5 is formed between the insulating layer 8 formed on the internal electrode 2 and the external electrode 3. More specifically, FIG.
As shown in (1), the stress relaxation layer 5 has a structure in which an inorganic porous body 6 having three-dimensionally continuous voids and a conductive substance 7 are mixed. Since the conductive substance 7 exists in the three-dimensionally continuous voids of the inorganic porous body 6 and has a three-dimensionally conductive path, the stress relaxation layer of the present embodiment does not impair the conductivity. In the present embodiment, since such a stress relaxation layer is provided, the residual stress caused by the amount of deformation and the difference in thermal expansion coefficient, which were problems of the conventional material, is reduced by the deformation of the inorganic porous material constituting the stress relaxation layer. Or by sliding deformation due to a conductive substance. In addition, by forming a laminated structure in which the inorganic porous body and the conductive substance are alternately laminated, slippage due to the conductive substance between the porous bodies also occurs, and the residual stress can be further reduced. Since the thickness of the stress relaxation layer varies depending on the physical properties of the inorganic porous material and the conductive material, it cannot be unconditionally determined, but is preferably smaller than 100 μm. This is because, when the thickness of the stress relaxation layer is more than this, residual stress due to the difference in thermal expansion coefficient between the stress relaxation layer and the piezoelectric material increases, and peeling occurs at the interface between the two.

The multi-layer piezoelectric element of this embodiment can operate at a higher temperature than a conventional multi-layer piezoelectric element, and can be used, for example, in a fuel supply device for an automobile engine.

As an example of the stress relaxation layer, a material in which an inorganic porous material containing silicon oxide as a main component and a conductive material containing conductive particles such as silver particles and palladium particles are mixed. As a method of forming such a stress relaxation layer, for example, a sol-gel method can be mentioned. That is, a sol solution containing conductive particles such as silver particles and palladium particles and a sol solution containing silicon oxide are applied and heated to form a stress relaxation layer. During the change from the sol state to the gel state, the solvent component in the gel solution was removed, and an inorganic porous body mainly composed of silicon oxide and a conductive substance containing conductive particles such as silver particles and palladium particles were mixed. A stress relaxation layer is formed.
Also, by alternately applying a sol solution containing conductive particles and a sol solution containing silicon oxide, a conductive material containing conductive particles such as silver particles and palladium particles and a porous body mainly containing silicon are formed. Alternately laminated structures can also be formed. Since the heating temperature varies depending on the components of the sol solution and the types and amounts of conductive particles such as silver particles and palladium particles, it cannot be said unconditionally, but is generally 500 ° C. or less. The heating temperature can also be reduced by irradiating each sol solution with light having a predetermined wavelength suitable for heating.

Next, the results of evaluating the characteristics of the material of the present example and the comparative material are shown.

In this embodiment, an organic binder is first added to a piezoelectric ceramic powder containing zirconate titanate (PZT) as a main component, and this is dispersed in an organic solvent to form a slurry. About 150μ
Make m ceramic sheet. A paste in which silver and palladium powders were mixed was formed on the ceramic sheet by screen printing. A predetermined number of the sheets were laminated, and finally, a ceramic sheet on which the above-mentioned paste was not printed was placed thereon, and the sheets were integrated by applying heat and pressure. This was cut into a predetermined size and then heated and fired to produce a laminate. Of the four side surfaces perpendicular to the stacking direction of the stacked body, a glass paste was applied and heated on the internal electrodes exposed on the two parallel side surfaces to alternately form an insulating layer for each layer. After alternately applying a sol solution containing 20% of silver particles and palladium particles and a sol solution containing 20% of silicon oxide to the side surface after forming the insulating layer,
Heating was performed at 0 ° C. for 30 minutes to form a stress relaxation layer. Thereafter, external electrodes and lead wires were formed on the stress relaxation layer. An inorganic high-temperature adhesive was used for the external electrodes, and a copper wire was used for the lead wires, and they were joined with the inorganic high-temperature adhesive.

As shown in FIG. 3, a comparative material for the present embodiment is obtained by forming an insulating layer on the side surface of a laminate manufactured in the same manner as in the present embodiment, and then forming the external electrode and the external electrode without forming a stress relaxation layer. Lead wires were formed.

As shown in FIG. 3, the laminated piezoelectric element has an internal electrode 2 connected to an external electrode 3 every other layer, and a lead wire 4 connected to the external electrode 3. When a voltage is applied between the lead wires 4, charges having different signs are induced between the internal electrodes 2 adjacent to each other, and a voltage is applied to the piezoelectric material 1 between the internal electrodes 2 to cause displacement in the laminating direction. In response to the deformation of the piezoelectric material 1, the external electrodes 3
Is hardly deformed, so that a residual stress is formed between the two due to the amount of deformation. When the laminated piezoelectric element is used at a high temperature, residual stress caused by a difference in thermal expansion coefficient between the piezoelectric material 1, the external electrode 3, the internal electrode 2, the external electrode 3, and the insulating layer 8 and the external electrode 3 is reduced. Between them, and there is a possibility that destruction may easily occur as compared with the case where the device is used near room temperature.

As an evaluation method, the material of this example and the comparative material were immersed in silicon oil heated to 150 ° C., and 100 V was applied with a sine wave having a frequency of 100 Hz to drive each element. As a result, while the comparative material was broken after the number of repetitions was 10 ⁶ times or less, the material of this example showed no abnormality even after 10 ⁸ times or more.

After an evaluation test of the material of this example, the stress relaxation layer was observed using a TEM (transmission electron microscope). As a result, as shown schematically in FIG. It showed a structure in which a porous body containing silicon as a main component and a conductive substance containing silver particles and palladium particles were mixed. The thickness of this stress relaxation layer was 10 μm or less. By the way, by increasing the coating amount of the sol solution containing silver particles and palladium particles and the sol solution containing silicon oxide, an element having a stress relaxation layer having a thickness of 100 μm or more was produced.
Immediately after being introduced into silicon oil heated to 50 ° C., peeling occurred between the piezoelectric material and the external electrode, and the evaluation was not completed.

In order for the conductive material constituting the stress relieving layer to exhibit a good lubricating effect and effectively work to reduce the residual stress, fine particles of the conductive material are contained in the conductive material. It is desirable. Also in the above evaluation experiment, the conductive material in the invention material contained silver particles and palladium particles having a particle size smaller than 1 μm. For comparison, a device containing silver particles and palladium particles larger than 5 μm in a conductive material was similarly prepared using a sol solution containing silver particles and palladium particles larger than 5 μm, and evaluated. the following breakdown has occurred 10 ⁶ times.

Further, the laminated piezoelectric element of this embodiment was incorporated into a fuel supply device of a gasoline engine, and an evaluation test as an actuator for gasoline injection was performed. Exam 12
At 0 ° C., the gasoline injection behavior was examined at an engine speed of 500 to 10,000 rpm. As a result, the gasoline injection response speed with respect to the input signal in all the rotation speed ranges is reduced by a factor of 1 / compared with the conventionally used electromagnetic actuator.
It was clarified that the material of the present example exhibited excellent characteristics as a fuel supply device part for an engine.

[0023]

According to the present invention, a highly reliable piezoelectric element can be provided even at a high temperature.

[Brief description of the drawings]

FIG. 1 is a schematic view of the structure of a multilayer piezoelectric element according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a structure near a stress relaxation layer of the multilayer piezoelectric element according to the embodiment of the present invention.

FIG. 3 is a schematic diagram of a structure of a multilayer piezoelectric element of a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric material, 2 ... Internal electrode, 3 ... External electrode, 4 ... Lead wire, 5 ... Stress relaxation layer, 6 ... Inorganic porous body, 7 ... Conductive substance, 8 ... Insulating layer.

Continued on the front page (72) Inventor Mitsuo Hayashibara 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hideo Suzuki 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Seiji Watabiki 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Tomio Ishida Omikamachi, Hitachi City, Ibaraki Prefecture No. 1-1, within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (6)

[Claims] 1. A multilayer piezoelectric element comprising a piezoelectric material having piezoelectricity and an electrode having conductivity being alternately laminated, wherein a stress relaxation layer is formed on a side surface perpendicular to the laminating direction. Piezoelectric element. 2. The multi-layer piezoelectric element according to claim 1, wherein the stress relaxation layer is a mixture of an inorganic porous material and a conductive substance. 3. The multilayer piezoelectric element according to claim 1, wherein the thickness of the stress relaxation layer is less than 100 μm. 4. A multi-layer piezoelectric element according to claim 1, wherein the stress relaxation layer contains particles having conductivity. 5. The multi-layer piezoelectric element according to claim 1, wherein the conductive particles contained in the stress relaxation layer have a particle size smaller than 5 μm. element. 6. A fuel supply device for an engine, comprising the multilayer piezoelectric element according to claim 1.